1. Field of the Invention
The present invention relates to an image scanning apparatus for use in, for example, copiers, scanners, facsimile machines and other suitable apparatuses, and more specifically, relates to improvement of a structure to adjust skew of a scanning unit.
2. Description of the Related Art
A variety of means for improving an adjusting structure have conventionally been proposed to resolve the skew of a scanning unit. For example, in an image scanning apparatus disclosed in Japanese Unexamined Patent Publication No. 2008-32942, adjustment clearance is formed between a guiding rod which guides a carriage in a vertical scanning direction and a rod-through hole provided at an attaching portion for the carriage, so that the adjustment clearance is used to conduct the skew correction. More specifically, a scanning unit is slanted in such a way that the scanning unit obliquely intersects with the vertical scanning direction when the scanning unit is not operating. When the scanning unit starts moving in the vertical scanning direction, the whole of the scanning unit is swung along the clearance formed for the skew adjustment in the direction opposite to the moving direction. In this way, displacing the whole scanning unit along the clearance formed for the skew correction can align a scanning line of an image sensor with the standard line.
In order to prevent a scanning line from being misaligned in processes for assembling an image scanning apparatus, the angle of mounting a guide rail on a platen has been adjusted using a jig, or the mounting state of a scanning unit on a guide rail has been adjusted using a jig. In this way, the position adjustment for a guide rail or a scanning unit in the assembling processes can, inmost cases, prevent deviation of a scanning line when the assembling is completed.
The skew correction structure described in the Japanese Unexamined Patent Publication No. 2008-32942 allows a scanning line of an image sensor to align with the standard line by intentionally displacing the whole scanning unit along the adjustment clearance, when the scanning unit moves in the vertical scanning direction. To this end, the rod-through hole of the attaching portion provided on the carriage needs to be formed with great accuracy and consequently costs a lot. Further, in a case where deviation of a scanning line occurs in a test scanning after an image scanning apparatus is assembled, a scanning unit needs to be separated from a guiding rod, a dry bearing provided on the rod-through hole needs to be adjusted and then the scanning unit needs to be reassembled. Consequently, a great deal of time and effort is required for the series of the adjustments required.
In this regard, with respect to an image scanning apparatus for which the angle of mounting a rail can be adjusted using a jig in an assembling process or an image scanning apparatus for which the mounting state of a scanning unit is adjusted in an assembling process, deviation of a scanning line can in most cases be corrected when the assembling is completed. However, as all such image scanning apparatuses need to be adjusted using a jig, a lot of time and effort is required to carry out the adjusting operations. Further, since a scanning line could be deviated by causes other than the mounting angle of a rail or the mounting position of a scanning unit, not all deviations of a scanning line can be avoided, requiring a structure that conducts some kind of correction.
Incidentally, deviation of an image scanning line occurring in an assembling process of an image scanning apparatus is in most cases within an acceptable error range, with few cases where the deviation of a scanning line is not within the acceptable error range. However, even if deviation of a scanning line hardly occurs, the deviation must be corrected. Consequentially, a structure capable of easily adjusting skew has been required.